'The end of the human race'. On the list of doomsday scenarios that could wipe out the human race, super-smart killer robots rate pretty high in the public consciousness.
All stars live by fusing hydrogen into helium. In the first step of the process, two hydrogen atoms fuse to form deuterium. In the next step, another hydrogen atom fuses with the deuterium, creating a rare isotope of helium that has two protons and one neutron in its nucleus. In the third step, two of the rare helium atoms fuse to create a single normal helium atom and two hydrogen atoms. The fusion pathway described above requires six hydrogen atoms to create one helium atomâhowever, there are two hydrogen atoms left over at the end of the process. The net result is that it takes four hydrogen atoms to make one helium atom.
Once all the hydrogen in the core has been converted to helium by nuclear fusion, there is no energy outflow to counter the inward force of gravity and the star rapidly collapses. This in turn heats the core and the region around it to such an extent that hydrogen fusion begins in the outer layers.